The present invention relates to an acceleration/deceleration control system of a servo motor used in a numerical control (NC) machine tool and a robot.
FIG. 1 is a block diagram of a servo motor acceleration/deceleration control system. A typical example of the conventional acceleration/deceleration system of this type is an exponential acceleration/deceleration control system.
In this system, an exponential function type acceleration/deceleration control unit is used as an acceleration/deceleration control section 1 shown in FIG. 1. When a position instruction is supplied as a displacement V.sub.0 per unit time to the acceleration/deceleration section 1, i.e., when a pulsed input shown in FIG. 2(a) is entered as a value V.sub.0 which is substantially the same as the velocity, an exponential output shown in FIG. 2(b) is obtained.
As shown in this response waveform, an acceleration speed is high at a leading edge (indicated by .alpha. in FIG. 2) due to the influence of a high-frequency component, so that a servo control section 2 and a load system are subjected to shock, resulting in vibrations. As shown in FIG. 2(b), a long period of time is required to decelerate and stop the servo motor, resulting in inconvenience. For these reasons, for example, when X- and Y-axis servo motors are used to shift a table of a machine tool in an arcuated manner, the table has a locus smaller than that designated by an instruction.
A linear acceleration/deceleration control system can be used in place of the exponential acceleration/deceleration control system. An output waveform shown in FIG. 5(b) is obtained in response to a step input shown in FIG. 5(a). As indicated by this output waveform, an acceleration speed abruptly changes, and a servo control system and a load system are subjected to shock, resulting in vibrations. For example, an arm of a robot or the like continues to vibrate when it is stopped quickly, resulting in inconvenience.
Furthermore, since the servo control system and the load system have natural frequencies, when the servo control system and the load system are driven by frequency components similar to their natural frequencies, respectively, the servo control system and the load system vibrate by themselves. For this reason, vibration of the natural frequency components included in position instruction for the servo control system and the load system must be cut off.